Valves in fluid circuits typically have an open state and a closed state, which is achieved by causing a linear actuator to extend towards, and press against, a membrane or diaphragm. In response, the diaphragm pushes into an orifice in the fluid pathway. The actuator continues to push the diaphragm into the orifice until the diaphragms contacts a valve seat opposite the actuator, thereby occluding fluid flow and closing the valve. The reverse process, namely moving the actuator away from the diaphragm and thereby releasing the diaphragm from compression against the valve seat, opens the orifice and permits fluid to flow. The linear actuator is typically driven by a stepper motor and/or DC motor operated by a controller. The system is preferably lightweight and consumes minimum power, making it ideal for use in a variety of applications. The system can be used in conjunction with an orifice in any structure. In particular, an orifice is any hole, opening, void, or partition in any type of material. This includes pathways in tubing, manifolds, disposable manifolds, channels, and other pathways.
Blood purification systems, which are used for conducting hemodialysis, hemodiafiltration or hemofiltration, involve the extracorporeal circulation of blood through an exchanger having a semi permeable membrane. Such systems further include a hydraulic system for circulating blood and a hydraulic system for circulating replacement fluid or dialysate comprising the certain blood electrolytes in concentrations close to those of the blood of a healthy subject. Flow in the fluid circuits is controlled by valves positioned in the fluid flow pathway. Examples of such fluid pathways include those disclosed in U.S. patent application Ser. No. 13/023,490, assigned to the applicant of the present invention, entitled “Portable Dialysis Machine” and filed on Feb. 8, 2011, which is incorporated herein by reference.
The valves are preferably implemented in a manifold using elastic membranes at flow control points which are selectively occluded, as required, by protrusions, pins, or other members extending from the manifold machine. In some dialysis machines, fluid occlusion is enabled using a safe, low-energy magnetic valve. Current valve systems often use a sensor, preferably an optical sensor, to determine the state of the valve (open or closed).
While the optical sensor is useful for determining the open or closed state of the valve and the position of the plunger, the prior art lacks a consistent and reliable mechanism for controlling the valve amidst changes in the valve system. Current linear actuators do not include a means for determining where or when to precisely stop pushing against the diaphragm (or membrane) in closing the valve, when to increase pressure to the diaphragm to keep the valve closed, or when to decrease pressure to a diaphragm that is being pulled via vacuum action in the fluid circuit. For example, over time, the diaphragm undergoes structural changes due to exposure to sterilization methods, temperature exposure, repeated strain, and pressure fluctuations within the system. Typically, the diaphragm material softens and thins. As these changes occur, moving the actuator to the same position results in incomplete shut-off of fluid flow. The actuator must be advanced further into the diaphragm to achieve the same level of valve closure.
A liner actuator driven by a stepper motor and/or DC motor operated by a controller can be used to deliver incremental changes to the actuator position. However, neither of these mechanisms allow for feedback control of actuator position through pressure or force sensing. Therefore, what is needed is an actuator mechanism for a manifold membrane/diaphragm type valve that allows for control of the positioning of the actuator based on feedback provided by a sensor located on the contact end of the actuator.